A Retrospective DNA Marker Assessment of the Development of Insect Resistant Soybean

characteristics (Lambert and Tyler, 1999). The lack of development of superior SIR cultivars may be due to There has been limited success over the past 30 yr in the developthe quantitative nature of resistance and to the retention ment of superior soybean cultivars [Glycine max (L.) Merr] with of undesirable PI donor alleles affecting any number insect resistance. Success may be hampered by the quantitative nature of resistance and by linkage drag from resistant plant introduction of traits because of their tight linkage with the insect (PI) donor parents. Soybean insect resistance quantitative trait loci resistance alleles, or QTL. This condition is often associ(SIR QTLs) have been identified from PI 229358 and PI 171451 ated with the use of nondomesticated germplasm for the by restriction fragment length polymorphism (RFLP) analysis. The introgression of novel alleles and is generally referred to objective of this study was to tag the SIR QTLs from PI 229358 with as linkage drag. simple sequence repeat (SSR) markers and to determine the extent The use of marker-assisted selection (MAS) could to which the SIR QTLs have been introgressed in registered cultivars, circumvent linkage drag by enabling concurrent selecgermplasm releases, or breeding lines that have resistance derived tion for SIR QTLs and against undesired genomic refrom this PI or from PI 171451. Marker analysis defined intervals by gions from a resistant PI during backcrossing. MAS 5 centimorgans (cM) or less for a SIR QTL on linkage group D1b could also reduce the need for phenotypic selection that (SIR-D1b), and for SIR-G, SIR-H, and SIR-M. SIR QTLs were tracked through pedigrees by evaluating the inheritance of PI alleles may be inefficient in identifying genotypic differences at marker loci tightly linked to the QTLs during the phenotypic selecfor SIR. Towards this end, Rector et al. (1998, 1999, tion for insect resistance. It was inferred that at least 13 of the 15 SIR 2000) used RFLP markers to map SIR QTLs from PI genotypes studied had introgressed SIR-M. PI genome introgression 229358 and from PI 171451. They detected a major SIR around SIR-M was measured to assess linkage drag. Some genotypes QTL conditioning antixenosis and antibiosis within a exhibited a dramatic reduction in the amount of linked PI genome, similar interval on linkage group (LG) M (SIR-M) from which likely occurred in response to phenotypic selection for agroboth PI 229358 and PI 171451. Another QTL associated nomic performance as a means of reducing linkage drag. Only a few with antixenosis in both PI 229358 and PI 171451 was genotypes were inferred to possess SIR-G or SIR-H, and no genotypes detected on LG H (Rector et al., 1998; 1999). From PI possessed SIR-D1b. The results of this study indicate that marker229358, SIR-D1b was detected for resistance on the assisted selection for SIR QTLs is needed to introgress these loci into elite genetic backgrounds. basis of antixenosis and SIR-G for antibiosis. SIR-D1b was not detected from PI 171451, and a lack of polymorphic RFLP markers limited detection of SIR-G. The SIR QTLs accounted for much of the variation for resisT development of soybean cultivars with insect tance in the mapping population, and they were found resistance (soybean insect resistance, SIR) has been to exhibit primarily additive gene action. While these an objective of several public breeding programs in the RFLP-based maps provide a framework for MAS of USA over the past few decades (All et al., 1999). Most SIR QTLs, the exact location of the SIR QTLs is not breeders have utilized Japanese PI 229358 or PI 171451 clear because of sparse RFLP marker coverage. Furtheras the initial donor parent for SIR (Lambert and Tyler, more, the use of RFLP markers for MAS in a breeding 1999). In a comprehensive review on SIR, Boethel et program is difficult because of their low polymorphic al. (1999) reported that these PIs were initially identified as content in soybean and their high technical demand. highly resistant to Mexican bean beetle [MBB; Epilachna Mapping the SIR QTLs with SSR markers, which are varivestis (Mulsant)], and later were characterized as abundant and polymorphic in soybean and practical for having resistance to several insect pests of soybean. high-throughput analysis, would facilitate MAS. They also indicated that SIR in both PIs is quantitatively Additional information on SIR QTLs could be obinherited and that they exhibit antixenosis (nonprefertained by determining the extent to which breeders usence) and antibiosis (detrimental effect on insect develing phenotypic selection for insect resistance have incoropment) resistance properties. porated the SIR QTLs into breeding lines or cultivars. There have only been three cultivars released with The availability of molecular linkage maps and pedigree SIR derived from a PI, and none of these cultivars has records provides an opportunity to track genomic rebeen widely accepted by growers because of inadequate gions through the breeding process (Shoemaker et al., resistance levels, inferior seed yield, or poor agronomic 1992). Young and Tanksley (1989) first used DNA marker-derived graphical genotypes of tomato (LycoJ.M. Narvel, Monsanto Company, Galena, MD 21635; D.R. Walker, W.A. Parrott, and H.R. Boerma, Dep. of Crop and Soil Sciences and Abbreviations: CEW, corn earworm; cM, centimorgan; LG, linkage J.N. All, Dep. of Entomology, Univ. of Georgia, Athens, GA 30602group; MAS, marker-assisted selection; MBB, Mexican bean beetle; 7272; B.G. Rector, USDA/ARS, Crop Genetics and Breeding RePI, plant introduction; QTL, quantitative trait loci; RFLP, restriction search Unit, Tifton, GA 31793. Received 13 Dec. 2000. *Correspondfragment length polymorphism; SSR, simple sequence repeat; SIR, ing author ([email protected]). soybean insect resistance; SBL, soybean looper; VBC, velvetbean caterpillar. Published in Crop Sci. 41:1931–1939 (2001).